1. Field of the Invention
The present invention relates to an angular velocity sensor for detecting the angular velocity of a rotator.
2. Description of the Prior Art
Referring to FIGS. 1 and 2, there are illustrated general arrangements of the prior art velocity sensors.
A first prior art example illustrated in FIG. 1 includes driving piezoelectric elements 2a, 2b disposed on outer side surfaces of plate vibrators 1a, 1b of a tuning fork vibrator 1, a detector 3 protruded on the bottom 1c of the tuning fork vibrator 1, and angular velocity detector means (not shown), each comprising a magnet and an electrode, etc., disposed on opposite side surfaces of the detector 3. The bottom 1c is coupled with a fixed plate 1e through a column (tuning fork shaft) 1d.
With such an angular velocity sensor an excitation signal is applied to the driving piezoelectric elements 2a, 2b to cause the plate vibrators 1a, 1b to vibrate with the same magnitude oppositely to each other as indicated by arrows V1, V2 in the figure. In this situation, once the tuning fork vibrator 1 is rotated counterclockwise around an axis Z, oppositely directed inertia forces (Coriolis forces) F1, F2 are generated perpendicularly to the direction of the vibration and perpendicularly to a rotation axis (Z axis). A torque due to the oppositely directed Coriolis forces F1, F2 is applied on the tuning fork vibrator 1 whereby the vibrator 1 exerts torsional vibration, the magnitude of the amplitude of which torsional vibration is detected by detector means (not shown) and is outputted as an angular velocity signal. A change in the amplitude of the torsional vibration of the tuning fork vibrator 1 is detected as a change in electrostatic capacity between a detector electrode provided in the detector means and another electrode disposed oppositely to the former.
The first prior art example described above has, however, has unsatisfactory detection accuracy and is generally too large. In contrast, another prior art example illustrated in FIG. 2 is contemplated to solve the difficulties with the first prior art example and is described in a reference (PROCEEDINGS FOR MICROELECTRO MECHANICAL SYSTEMS Feb. 7-10, 1993). An angular velocity sensor in the same figure is formed using a semiconductor substrate such as a silicon substrate with the aid of a semiconductor microprocessing technique. A fixed electrode 5 is formed at the center on a substrate 25, and vibration plates 7, 8 of a tuning fork vibrator are disposed on the left and right sides of the fixed electrode 5 in a floating state with their corners 7a, 7b, 8a, 8b coupled to a fixed portion 14c, and electrodes (not shown) are disposed on an opposed surface to the substrate 25 and the vibration plates 7, 8 floating from the substrate 25. A plurality of holes 9 are formed in the vibration plates 7, 8, and comb electrodes 10a, 10b, 11a, 11b are provided on the left and right sides of each vibration plate 7, 8, protruding from the same sides. Comb electrodes 5a, 5b are likewise formed on the fixed electrode 5, which are disposed putting slight spaces between them and the comb electrodes 10a, 11a of the vibration plates 7, 8.
In the angular velocity sensor arranged as described above, a vibration driving signal is applied between the comb electrodes 5a, 5b of the fixed electrode 5 and the comb electrodes 10a, 11a of the vibration plates 7, 8 to vibrate the vibration plates 7, 8 oppositely but with the same magnitudes indicated by V1, V2 in the figure. In this situation, once the vibration plates 7, 8 are rotated counterclockwise around an axis Y, there are produced opposite inertia forces (Coriolis forces) F1, F2 perpendicular to the directions of vibrations and to the axis Y. The opposite Coriolis forces F1, F2 cause torsional vibrations of the vibration plates 7, 8, changes in the amplitudes of which torsional vibrations are detected as changes of electrostatic capacities between electrodes disposed in opposition on the substrate 25 and the vibration plates 7, 8. The changes are outputted as a detection signal of an angular velocity.
In accordance with the second prior art example, as described above, it is fabricated with use of a microprocessing technique and hence is miniaturized with very excellent processing accuracy compared with the first prior art example.
When such an angular velocity sensor is contemplated to be formed with a semiconductor, it is possible to fabricate it with a higher Q owing to excellent mechanical characteristics of semiconductors. In the second prior art example, however, there is a possibility of the Q being deteriorated as described above. In the second prior art example, the vibration plates 7, 8 of the tuning fork vibrator are directly coupled with the fixed portion 14c through the corners 7a, 7b, 8a, 8b, so that severe distortion is produced between the corners 7a, 7b, 8a, 8b and the direct coupled portions owing to the torsional vibrations produced on the vibration plates 7, 8. Hence much of the vibration energy serving to cause the torsional vibrations is wastefully consumed as external transmission energy from the fixed portion 14c. Accordingly, the Q concerning the torsional vibration of the tuning fork vibrator is reduced thereby resulting in deteriorated detection resolution.
Further, in the angular velocity sensor illustrated in FIG. 1, which comprises a material such as metal and is fabricated through a mechanical processing, it is difficult to improve the Q, and in addition since the plate vibrators 1a, 1b are coupled with the fixed plate 1e through the bottom 1c and the column 1d, much of vibration energy serving to cause the torsional vibrations on the plate vibrators 1a, 1b is wastefully consumed as external transmission energy toward the fixed plate 1e through the bottom 1c and the column 1d. The Qs of the plate vibrators 1a, 1b are further reduced making it difficult to obtain an angular velocity sensor with a higher angular velocity resolution.